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Wood structures: story shear & unit shear question

  1. Nov 27, 2007 #1
    1. The problem statement, all variables and given/known data

    A rectangular two-story building with a wood roof and floor system and masonry walls is analyzed to determine seismic forces.

    Given: I=1, roof dead load D=15psf, floor load=25psf including partition load. Exterior wall dead load D=80 psf along both long and short walls. Ta=0.189seconds. SDS=0.4g and SD1=0.145. Redundancy factor is 1.0. R=5 for a bearing wall system with special reinforced masonry shearwalls.

    The story height is 12 ft each floor. Additional 2ft of parapet is above the roof. Assume the masonry walls are along both long and short direction. The story dimension is 100'x40'

    a.) Determine the story shear on shear wall between roof and second-floor level along short walls.
    b.) Determine the unit shear in roof diaphragm along short walls.

    2. Relevant equations

    Cs=SDSI/R=0.08g (given)
    k=1 because 0.189s < 0.5s

    Fx Coefficient=(0.08*608)wi*hi=0.00478

    3. The attempt at a solution


    Weight of Roof:
    Tributary Weight of Roof: 1880plf*100'+(12'/2+2')(80psf)(40')*2=239.2kips

    Weight of 2nd Floor:
    Tributary Weight of 2nd floor: 2920plf*100'+2(12'/2+12'/2)*40'*80psf=368.8kips


    Roof Reaction:
    2nd Floor Reaction:

    Mid-story shear=10.81+(0.115*80*(12;/2+2)*40)=13.754kips


    Weight of Roof=2920plf
    Wupr=(0.115)*2920=335.8 lb/ft
    Vur=(Wupr*L)/2=(335.8*100)/2=16790 lbs
    vur=Vur/b=16790/40=419.75 lb/ft

    Could anyone please check if I'm doing this correctly? I'm very uneasy about this answer, not because it doesn't sound right, but I'd really like to have this correct or find out what I'm doing wrong. Thanks ahead of time!
  2. jcsd
  3. Nov 29, 2007 #2
    bump. this is done using ASD in california.
  4. Dec 1, 2007 #3


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    Hey mrmotobiker,

    My wood structure design is a little rusty, but i'll give it a try.

    So far your calculations look correct. I might that for the tributary second floor loas a partition load is usually added about 10 psf for seismic design force, but maybe you don't have to add it.

    So far your a) part looks ok. Another method for obtaining the shear at midheight of second-story walls only for a simple rectangular building with two equal transverse shearwalls is by dividing the total roof shear by 2.

    Now part b) looks weird to me.
  5. Dec 14, 2007 #4
    thanks. i got part a right, used the wrong weight for part b.
  6. Dec 17, 2007 #5
    hey cyclovenom, i realized we're the same age (your profile) lol. what school do you go to? i'm really looking into grad school for structural as well.
  7. Dec 17, 2007 #6


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    Hey motorbiker, i'm dominican and i studied (graduated already) at http://www.unibe.edu.do" [Broken] . I'm planning on going to GATech on 2008 summer.
    Last edited by a moderator: May 3, 2017
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